Tumble pattern sensor and method of drying



April 2l, 1970 w. F. RQBANDT. .Y ,3,507,05

TUMBLE PATTERN SENSOR AND METHOD OF DRYING v Filed March 2o, i968 w 3sheets-sheet 1 E 75 El 2g-Z TUMBLE PATTERN SENSOR AND METHOD OF DRYINGF11-ed March 2o, 1968 April 21, 1970 w. F. RQBANbT INVENTOR.

3 Sheets-Sheet Z April 21, 1970 A w. F. RQBANDT A 3,507,052 l TUMBLEPATTERN- sEN'soR Nn METHODOF DRYING- l 3 Sheets-Sheet 3 INVENTOR.

\ gm F'- gamma Filed March 20, 1968 d y'. ATTORNEYS United States PatentOffice 3,507,052 Patented Apr. 21, 1.970

,507,052 TUMBLE PATTERN SENSOR AND METHOD F DRYING William F. Robandt,St. Joseph, Mich., assignor to Whirlpool Corporation, St. Joseph, Mich.,a corporation of Delaware Filed Mar. 20, 1968, Ser. No. 714,581 Int. Cl.F26b 7/00, 13/10 U.S. Cl. 34-12 25 Claims ABSTRACT OF THE DISCLOSURE Adryer apparatus in which materials are tumbled in a treatment zone andwherein sensing means sense variations in the tumble pattern of thematerials so that the drive motor may be driven at a speed insuring anoptimum tumble pattern. The control is effected by regulating eithermotor speed or by actuating a magnetic slip clutch as a function ofchanges in tumble pattern. Moisture sensing controls are also provided.

CROSS REFERENCE TO RELATED APPLICATION The tumble pattern sensor andmethod of drying of this invention is applicable to dryers such asdescribed in the application entitled Hold Circuit for a Dryer, inventedby William F. Robandt and Keith D. Salisbury and assigned to theassignee of this invention, Ser. No. 718,432, filed Apr. 3, 1968.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesin general to dryers, as for example, clothes dryers formed with rotarydrums or other mechanical means which tumble clothing or other materialthrough a drying air stream. A control system has sensing means in theair outlet of the dryer 4which controls the tumble speed and turns offthe dryer when a preset moisture level has been obtained. The tumblespeed is controlled so that the articles being dried follow an optimumtumble pattern.

Description of the prior art U.S. Patent 3,072,386 sets the drum speedof a clothes dryer in response to the weight of clothing added. U.S.Patent No. 3,266,168 has a preset table motor speed control which holdsdrum speed at a single speed throughout a cycle of operation.

SUMMARY OF THE INVENTION In accordance with the present invention,sensing means are provided to sense variations in a tumbling patternwithin a treat-ment zone. The resultant signal is used to control drumspeed, thereby to insure that an optimum tumbling pattern is obtained.For example, the tumble pattern is sensed within a treatment zone -bydetermining conditions at two or more discrete locations in a tumblingdrum. Such determination is effected by temperature sensing means, airpressure responsive means or photoelectric means. The drum speed is thencontrolled as a function of variations in the tumble pattern by eithercontrolling the speed of the drive motor or controlling the operation ofa magnetic slip clutch.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE l is a somewhat schematic frontelevational view of a dryer embodying the features of the presentinvention;

FIGURE 2 is a side elevational view of the dryer of FIG. l;

FIGURE 3 is an enlarged view of a control panel of the dryer;

FIGURE 4 is a fragmentary cross sectional view taken on line IV-IV ofFIGURE 2 showing the back wall of a dryer constructed in accordance withthis invention and showing various tumble patterns which exist in thetreatment zone prescribed by the machine of FIGURES l and 2;

FIGURES 5a and 5b are additional detailing schematics of the controlsystem of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGUR-ES 1 and 2 are schematicviews of a clothes dryer 11 which has a cabinet 12 with a door 13. Thedryer 11 is of the so-called stationary bulkhead type more particularlydisclosed and claimed in U.S. patent application S.N, 425,302; led Jan.13, 1965, and assigned to Whirlpool Corporation, assignee of the presentinvention. A control panel 15 is attached to the top of the cabinet 12and has a moisture control knob 14 and a start button 16. Asbest shownin FIGURE 3 the knob 14 has a pointer 17 that may be set against indicia20 to control the shut-olf point of the dryer in accordance with apreset selection depending on the degree of dryness desired by theoperator. In a stationary bulkhead dryer of the type shown onlyschematically herein, a stationary rear wall 18 forms one wall of atreatment zone. The peripheral contines of the zone are formed by arotatable drum wall 19 driven by a motor 21 and a belt 22. With such anarrangement, a batch of clothes or other material placed within thetreatment zone will be tumbled for exposure to a stream of air directedtherethrough.

It is well known that the speed of rotation of a drum has a profoundeffect on the tumble pattern in the treatment zone. For example, if thedrum is rotated at a speed suiciently high that it is beyond acritically determinative speed for the diameter of the drum, thematerials will merely adhere to the surface of the drum in the form ofan annulus and will not tumble at all.

On the other hand, if the drum is rotated at slow speed, the materialswill merely roll over in the bottom of the drum. Under suchcircumstances clothes tend to ball and will not be properly exposed todrying currents of air as to promote evaporation of the entrainedmoisture.

In accordance with this invention it is contemplated that an optimumtumbling pattern will be achieved. The optimum pattern is such as willpermit the materials in the drum to be elevated by the rotating drumwall through a lower quadrant of a cylindrical zone inwardly of the drumwall and on upwardly into an upper quadrant of the cylindrical zone. Thespeed of the drum is closely regulated so that the dynamic forcesimparted to the materials being tumbled will elevate the materials to anoptimum discrete location in the upper quadrant whereupon thegravitational forces acting on the materials will overcome the applieddynamic forces and the materials will fall in a trajectory extendingmore or less diametrically y y 3 acrossvrthe V,cylindricalzone formaximum exposure to currents of drying air circulating through the zone.The materials impact against an oppositely disposed lower quadrant ofthe drum wall, whereupon they are once again acted upon by the rotatingdrum wall.

An inlet orifice 23 and an outlet orifice 24 are fformed in the bulkhead18, A heater 10 is mounted in a duct (not shown) leading to the inletorifice 23 and a Vblower motor 26 with a suitable impeller is mounted ina duct (not shown) leading from the outlet orice 24 to draw a supply ofheated drying air in the form of a stream through the dryer. AlthoughFIGURE 4 illustrates a totally stationary bulkhead, it will beunderstood that only a portion of the bulkhead may be made stationary ifit is so desired.

As shown in FIGURE 4, and in accordance with this invention the outletorifice 24 is generally above center and to one side of the dryer. At afirst discrete predetermined location arrows X, Y, and Z illustratevarious paths which articles in the dryer -will take depending oncorresponding drum speed. For example, arrow X shows a path where thematerials being tumbled begin the gravitational trajectory near the topof the orifice and results when the drum speed is relatively high. Thearrow Y depicts a trajectory which passes generally over the center ofthe outlet orifice 24. When the material to be dried follows a pathbetween trajectories X and Y, optimum drying performance results sincethis path maximizes the exposure of tumbling materials to currents ofdrying air. The arrow Z illustrates a path wherein the gravitationaltrajectory begins below the orifice 24 and corresponds to a drum speedwhich is too slow for optimum drying conditions. Thus, to maintain anoptimum tumbling speed, the drum speed must be continuously adjustedthroughout the drying cycle so clothing always follows the path betweenarrows X and Y in tumbling through the heated air circulated through thedrum. An additional benefit of this control system is that as the drumspeed is continuously varied to induce clothing or other tumbledmaterials to follow the trajectory between arrows X and Y, the changingspeed breaks up any regular tumbling pattern the clothing mightestablish thereby causing it to ball This balling effect is highlydetrimental to proper drying since the clothing on the inside of theball is not exposed to heated air and comes out damp while the clothingon the fringes of the load are over-dried.

j In order to maintain the articles being dried in the band shownbetween arrows X and Y to obtain optimum drying, the speed of the drummotor 21 is controlled to maintain the material in this band by means ofsensing means determining the tumble pattern at two discrete lo- :ationsinwardly of the drum wall. A pair of transducers 28 and 29 are mountedin the outlet orifice 24 with transducer 29 mounted adjacent the top ofthe orifice and transducer 28 mounted adjacent the bottom of theorifice. Transducers 28 and 29 may be thermistors, for example, althoughthe invention is not to be limited to thermistors as other forms ofsensing means such as thermostats, air Jresfsure switches, photocells orlamp sensors could be Jsed.lIf clothing follows the arrow Y, heated airmust pass through damp clothing before going out the portion 3f thegrillin which thermistor 28 is located. However, heated air does not gothrough the clothing load before passing `by thermistor 29. Thus, ifclothing follows, the arrow Y, thermistor 28 typically runs about 10 F.cooler :han thermistor 29. To control the drum speed so that thepathbetween arrows X and Y is followed by the clothing, therefre, a`speed control circuit for the motor receives inputs from thermistors 28and 29 and continuously varies die drum speed so that the temperaturedifferential be- ;ween thermistors 28 and 29 is maintained at thedeterninable maximum as evidenced between the two discrete locations.

As the clothing within the drum begins to dry, hot air Jassing throughthe partially dried clothing no longer is cooled as much as it was atthe beginning of the cycle when the clothing was completely soaked.Thus, near the end of the drying cycle thermistor 28 begins to approachthermistor 29 in temperature. I have determined that the temperaturedifferential between thermistors 28 and 29 is linearly related to thepercent moisture retention of the load when it follows the pathintermediate arrows X and Y. Thus, by using the temperature differentialbetween the two thermistors, a source of signal for an extremelyaccurate dry control responsive to variations in the tumble pattern isobtained.

In a typical operation of a domestic clothes dryer controlled by thecircuitry of theinstant invention, the housewife sets knob 14 to thedesired moisture retention and presses start button 16 to start thedryer. As -best shown in FIGURES 5a and 5b commonly available A.C.power, as for example volts, is connected between terminals B and N ofthe dryer. A 220 volt supply is connected between terminals B and C. Adoor switch 31 is connected to terminal B and is open when the door 13is open. When the door 13 is closed, the switch 31 closes to connectterminal B with contact 32 of switch 16. Contact 32 is connected to athermostat switch 33 which is in series with a centrifugal switch 34,actuated when motor 21 comes up to normal operating speed, a relayactuated heater switch 36 and the heater 10. The outer side of theheater 10 is connected to terminal C.

A second terminal 37 of switch 16 is connected to a hold relay 38 whichhas its other side connected to terminal N. The relay 38 has an armaturewhich moves the linkages 35 to control the switches 36 and 39.

The switch 39 has one contact connected to the contact 32 of the switch16. A second contact 41 is connected to a lead 42. A cool-downthermostat 43 is connected between the contact 32 and the lead 42.

A normally closed switch 44 has one contact connected to contact 41 anda second contact 46 connected to one side of relay 38. The motor 21 hasa run winding 47 and a start winding 48. First sides of these windingsare connected to the lead 42. The other side of the winding 48 isconnected to a centrifugal switch 49 which opens when the motor comes upto speed and has its other side connected to a capacitor C1. The otherside of the capacitor C1is connected to terminal N. A condenser C2 isconnected from the terminal N to the winding 48. A triac 51 has theanode thereof connected towinding 47 and its cathode connected toterminal N. The gate lead 52 of triac 51 is connected to a resistor R1and the anode of a diode D1. The cathode of diode D1 is connected to thesecondary 53 of a transformer T1. The other sides of secondary 53 andresistor 'R1 are connected to the terminal N.

A full wave bridge 54 comprising diodes D2, D3, D4 and D5 is connectedbetween terminal N' and a resistor R3. The other side of resistor R3 isconnected to lead 42.

A resistor R2 is connected between diodes D2 and D3 and.

lead 54. A lead S6 is connected between diodes D4 and D5. A Zener diodeD6 is connected v.between leads 54 and 56. A capacitor C3 is connectedacross Zener diode D3.

The primary 57 of transformer T1 is connected to line 54 and to thecollector of a transistor T10. The emitter of transistor T10 isconnectedto a resistor which has its other side connected to lead S6. Aresistor R5, a unijunction transistor T3 and a resistor R6 are connectedin series between leads 54 and 56.

A variable resistor R7 and a capacitor C11 are connected between lines54 and 56. The emitter Lelectrode of transistor T3 is connected to thepoint betweenl resistor R7 and capacitor C11. A diode D7 has its cathodealso connected to this point and its anode connected to resis? tors R8,R9 and the collector of transistor T2. The other side of resistor R8 isconnected to lead 54. A resistor R11 is connected between the emitter oftransistor T2 and lead 56. The other side of resistor R3 is connected tothe base of transistor T2.

A resistor R19 isalso connected to the base of transistor T2 and topoint H. A condenser C4 is connected between point H and lead 56.

Referring to FIGURE 5b it will be noted that points D, E, H, F and Gcorrespond to the same points in FIG- URE 5a.

The motor 21 has an output shaft 58 which drives a tachometer 61. Thetachometer 61 provides an A.C. input voltage to a bridge 62. Thetachometer 61 has an output coil 63 connected across points M and O ofbridge 62. Resistor R13 is connected between points Q and O yandResistor R14 is connected between points O and P. Thermistor 28 isconnected between points M and P and thermistor 29 is connected betweenpoints M and A resistor R12 is connected between point Q and lead 56. Awiper contact 65 engages resistor R12 and is connected to the anode ofdiode D14. The cathode of diode D14 is connected to resistor R19. Aresistor R15 and capacitor C12 are connected in series between point Qand the base of a transistor T3.

A transformer T29 has its primary 64 connected between leads 42 and 56.The secondary 66 of transformer T29 is connected across a full wavebridge 67 having diodes D5, D9, D19, and D11. A resistor R15 isconnected between diodes D9 and D19 and to lead 68. A capacitor C5 andZener diode D12 are connected in parallel between leads 68 and 69.

Resistors R17 and R19 are connected in series across leads 68 and 69. Acondenser C5 is connected across resistor R19. The junction pointbetween resistors R17 and R19 is connected to the base of transistor T3.Resistor R13 is connected from lead 68 to the collector of transistorT3, and a resistor R29 is connected between the emitter of transistor T3and lead 69.

Resistor R21 and capacitor C3 are connected in series between leads 68and 69. Resistor R22 is connected between the emitter of transistor T3and the junction point between resistor R21 and capacitor C9. CapacitorC7 is connected across R21.

A resistor R23, transistor T5 and capacitor C19 are connected in seriesbetween leads 68 and 69. A resistor R25 is connected across condenserC19. A resistor R25 is connected between lead 68 and the base oftransistor T5.

A Zener diode D13 and resistor R24 are connected in series between thecollector of transistor T5 and the point between resistor R21 andcondenser C5.

A capacitor C9, transistor T4 and relay 71 are connected in seriesbetween leads 68 and 69. The base of transistor T4 is connected tocapacitor C19.

The relay 71 controls linkage 59'. A wiper arm 72 is connected to theemitter of transistor T4 and forms a part of potentiometer 73. This isthe moisture control element and knob 14 is connected by shaft 74 tocontrol the position of wiper arm 72. A resistor VR27 is connectedbetween line 68 and potentiometer 73. 3

In operation, the speed of motor 21 is maintained so that an optimumtumbling pattern is established. The user places clothing or otherarticles to be dried in the dryer and sets pointer 17 by knob 14 to thedesired final moisture content of the articles. This sets wiper arm 72of potentiometer 73 to a particular resistance.

The door 13 is closed which closes door switch 31 and the start button16 is momentarily depressed to engage contacts 32 and 37. This suppliespower to relay 38 which closes switches 36 and 39. Switch 39 suppliesholding current to relay 38 through normally closed switch 44.

The heater 10 will be energized through normally closed safetythermostat 33 and centrifugal switch 34 when the motor 21 comes up tospeed.

Switch 39 also provides power on line 42 to a motor speed controlcircuit and a dry control circuit. Normally open thermostat switch 43 isopen unless the temperature in the exhaust stack of the dryer reaches ahigh temperature as, for example, 110 F.

Both the motor speed control and the dryer control receive signals fromthe bridge circuit 62.

The motor 21 starts with normally closed centrifugal switch 49 allowingcurrent to pass through the start winding 48. As the motor comes up tospeed, switch 49 opens and the run winding 47 continues to energize themotor.

The tachometer 61 is driven by motor 21 through shaft 58. The tachometerinduces a voltage in winding 63 which varies in frequency and magnitudewith the speed of motor 21.

Bridge 62 includes thermistors 28 and 29 (see FIG' URE 4 for theirmounting positions) and resistors R13 and R14. Resistor R13 has a lowerresistance than resistor R14. When the dryer starts the resistance ofthermistors 28 and 29 are the same due to their resistance versustemperature curves being identical. Thus, at the initiation of thecycle, a signal voltage appears at point Q. Also, any time that theresistance of thermistor 28 approaches the resistance of thermistor 29,a signal voltage will appear at point Q because of the initial unbalanceof the bridge. It should be remembered that the voltage at point Q. ofthe bridge depends on two factors, (l) the speed of motor 21 and (2) thetemperature diiference between thermistors 28 and 29.

The signal voltage at point Q is utilized to regulate the speed of motor21 so that if the tumbling pattern is maintained at the optimum, thissignal controls the firing point of triac 51 which regulates powersupplied to run winding 47 in the following manner.

Voltage for the motor speed control is supplied by line 42 throughresistor R3. This is full wave rectified by bridge circuit. The fullwave rectied A.C. then passes through a current limiting resistor R2 andis applied to iilter capacitor C3 whose output voltage is clipped byZener diode D5.

Capacitor C3 has a small capacitance so that it does not maintain a setlevel of ripple-free D C. voltage on line 54. Instead, this voltagerises and falls, giving a generally clipped full wave signal, as shownby curve 78 above line 54. This is important because triac 51 must befired at a controlled point in each half cycle of A.C. power and thefiring point must be synchronized to power on the A.C. line.

Wiper arm 65 is set on resistor R12 to preset a desired voltage. Thisvoltage is half wave rectified by diode D1.,= and furnished to ltercapacitor C4. The voltage across capacitor C4 is thus proportional tothe signal voltage at point Q.

The voltage on capacitor C4 supplies base drive to transistor T2.

If the signal voltage at point Q is high, transistor T2 will be driveninto saturation and the voltage appearing at its emitter will be low.Thus, current passing through resistor R9 each time the voltage rises atpoint Q is shunted to ground through transistor T2 and does not passthrough diode D7 to capacitor C11. All charge current to capacitor C11must pass through resistor R7. Resistor R7 is set such that the voltagelevel on capacitor C11 builds at a slow rate. At a predetermined level,the voltage on capacitor C11 res unijunction transistor T5 and thecharge dumps from capacitor C11 through transistor T5 and resistor R5.This creates a voltage drop across resistor R5 which biases switchingtransistor T19 on. A current pulse is then drawn through the primary 57of pulse transformer T1. This generates a pulse across the secondary 53ofthe pulse transformer and triac 51 is fired through diode D1. Oncetriac 51 fires, power is delivered to the motors run winding 47. Notethat a high magnitude of signal voltage at point Q results in delayedtiring of triac 51 and motor 21 is caused to run at a low speed.

If the output voltage at point Q is low (which is the case when bridge62 is balanced due to thermistor 29 being hotter than thermi-stor 28thereby insuring that its resistance is lower than thermistor 28, orwhen the motor is rotating slowly causing tachometer 61 to generate alow voltage) capacitor C4 will have a low voltage appearing across it.This biases transistor T2 to a nonconductive state and current passes tocapacitor C11 via re-sistor R8 and diode D7, as well as through resistorR11. This insures that unijunction transistor T is red early in eachhalf cycle and thus triac 51 tires early in each half cycle. The motor2.1 now runs at a higher rate of speed due to the increased powersupplied to run winding 47. In summary, with signal voltage low at pointQ, thc motor runs at a relatively high rate of speed.

As shown in FIGURE 4, it is to be noted that the tumble pattern of theclothing should follow a trajectory lying somewhere between the arrows'X-and Y. The control circuit of this invention assures this in thefollowing manner. When the drying cycle is initiated, thermistors 28 and29 are of cour-se, at equal temperatures. This causes the bridge 62 tobe unbalanced and the output at point Q tends to be high due to theeffect of the thermistors. This effect alone would tend to slow themotor down and the clothing would be expected to follow the arrow Z.AHowever, with the clothing following the arrow Z, the motor is rotatingat such a low speed that tachometer 61 applies a very small voltage tobridge 62. Although the thermistor bias tends to slow the motor down,the input to the bridge is so low that no appreciable signal appears atpoint Q. Thus, the motor control circuit applies ring pulses to triac 51early in each half cycle of the A.C. line and motor 21 speeds up. Theclothing is thus not allowed to follow the path of arrow Z simplybecause bridge 62 will be supplied with insufcient voltage to produce anoutput of any magnitude at point Q with the motor rotating at such aslow speed.

Assuming the rnotor is rotating at a higher speed, which causes theclothing to follow the trajectory of arrow X, both thermistors 28 and 29are covered by the clothing. Thus, their temperature and resistancebecome equal. Due to the different resistance of resistors R15 and R14,a high signal voltage appears at point Q. Also, since motor speed ishigh, the magnitude of tachometer output is high causing the input tothe bridge to be high. Thus, both bridge unbalance and high motor speedcause the output at point Q to be high. Capacitor C11 now charges to ahigh value and saturates transistor T2. This insures that the tiringpulse delivered to triac 51 via pulse transformer T1 is delayed in eachhalf cycle of A.C. line voltage, causing motor 21 to slow down. Thus,clothing no longer follows the path of the arrow X.

When the clothing follows the path of arrow Y, the thermistor 28 isshielded from hot air passing through orifice 24 while thermistor 29receives hot air. This Causes thermistor 29 to heat above thermistor 28and its resistance value drops. Bridge 62 now tends toward balance andthe output voltage at point Q decreases.

The charge level on capacitor C4 decreases correspondingly andtransistor T2 begins to go out of saturation. This allows earliercharging of capacitor C11 in each half cycle of A.C. line voltage andthe triac 51 is iired earlier. Thus, the motor speeds up. By thisaction, the clothing is caused to continuously oscillate in a band lyingbetween arrows X and Y.

It should be noted that when clothing is rst placed in the dryer, thedrum sped for an optimum tumble pattern is different than the drumspeedfor an optimum tumble pattern near the end of the drying cycle after theclothing has nearly dried. It has been found that the average drum speedmust increase as the cycle progresses to keep the clothing in the banddefined by arrows X and Y. The speed control of this invention regulatesthe average drum speed such that it does increase throughout the cycleof operation thereby maintaining an optimum tumble pattern throughoutthe cycle. It is also noted, that since the clothing is forced tooscillate in a band between arrows X and Y, any established tumblingpatterns are broken up and the clothing is always placed directly in thepath of the heated air. This not only assures minimum drying time butalso assures that the clothing will not ball which would lead tooverdrying of the outside of the load while the inside remained damp.

The dry control portion of the invention is shown in FIGURE 5b. Thevoltage at -point Q is also used to control the termination point of thedrying cycle. Power on line `42 passes through the primary 64 ofstepdown transformer T20 and -appears on the secondary 66 at -a reducedvoltage. Bridge circuit 67 full wave recties the output of transformerT20 and applies it to a filter capacitor C5 via current limitingresistor R15. Zener diode D12 regulates the voltage across capacitor C5to a D.C. level con-sistent with the ratings of components within thedry control circuitry.

Potentiometer 73 forms part of a voltage divider consisting of a fixedresistor R21, potentiometer 73, and relay coil 71. Thus, the initialsetting of potentiometer wiper 72 determines the emitter voltage oftransistor T4. Transistor T4 is connected in a regenerative fashion withtransistor T5. If a voltage of magnitude greater than the emittervoltage of transistor T4 appears at the base of transistor T4 it beginsto conduct. This draws base current from transistor T5 which also beginsconduction. As transistor T5 goes into conduction, the base drive totransistor T4 is reinforced and the pair of transistors cascade intoconduction. When these two transistors -become conductive, the dryingcycle is terminated as described below.

The time when transistors T5 and T4 cascade into conduction iscontrolled by the signal voltage at point Q which is A.C. coupled to thebase of transistor T3 via a resistor R15 and capacitor C12. As long asthe clothing within the drum is damp, the motor speed control insuresthat it oscillates within the band dened by arrows X and Y. Whenclothing follows arrow Y, output at point Q is low and the voltagecoupled to transistor T3 is correspondingly low. Thus, transistor T3does not conduct and charge does not pass to capacitor C3 throughresistor R22. When clothing follows the path of arrow X, output at pointQ causes transistor T3 to conduct and charge begins to accumulate oncapacitor C5. However, as long as clothing within the drum is damp, itcools thermistor 28 when clothing follows arrow Y. This assures that thecharge applied to capacitor C5 while the clothing followed arrow X isbled away from the capacitor while the clothing follows arrow Y.

This alternate charging and discharging of capacitor C8 does not allowthe voltage at point U to rise to a level exceeding the Zener voltage ofZener diode D13 and thus current does not pass through Zener diode D13and resistor R24 to circuit point V. This assures that with dampclothing in the dryers drum, transistors T4 and T5 are not cascaded intoconduction. However, as the clothing begins to dry, thermistor 28 is notcooled by clothing following arrow Y and the resistance of the twothermistors begins to equalize. Now the signal voltage at point Qremains at a high level for an extended period of time. This signalvoltage is continuously coupled to transistor T3 and it remainsconductive on a continuous basis. Thus, the charge level on capacitor C3builds until it rises above the Zener voltage of Zener diode D13.Current now passes to circuit point V and transistors T4 and T5 cascadeinto conduction. The amount of current which must be supplied at point Vto cascade the two transistors is determined by the emitter bias ontransistor T4 which is, of course, preset by potentiometer 73. Thispermits the termination point of the drying cycle to be varied bypotentiometer 73 and thus the final moisture retention of the clothingmay be varied.

When transistors T4 and T5 cascade into conduction, relay coil 71 isenergized, thereby opening switch 44 and breaking power to relay coil38. When relay coil 38 drops out, contacts 36 and 39 open. This breakspower to the machines heater 10. However, note that normally opencool-down thermostat 43 has closed during the drying cycle since theexhaust stack temperature has risen. Power continues to be suppliedthrough thermostat 43 to line 42. This keeps rotor 21 running until theexhaust stack temperature drops far enough for thermostat 43 to open,whereupon the cycle of operation is terminated and the clothes may beremoved from the machine.

The following modifications could be made to the system described abovewithout departing from the spirit and scope of the invention.

(l) Thermistors 28 and 29 could be replaced with appropriatelycalibrated thermostats which would allow the motor speed to be variedbetween two distinct levels in accordance with the tumble pattern ofclothing sensed within the drum.

(2) Thermistors 28 and 29 could be replaced with pressure switches whichsense the velocity of exhaust air passing through different locations inthe exhaust outlet. These switches could then mechanically controlpotentiometers in bridge circuit 62 to control motor speed in the samemanner as thermistors 28 and 29.

(3) Thermistors 28 and 29 could be replaced with photocells andappropriate light sources to sense the tumble pattern within the drum.As clothing blocked light from the photodiodes in a selective manner,motor speed would be controlled to give an optimum tumble speed.

(4) The control circuit could be used to control a magnetic clutchinterposed between drive motor 21 and the dryers drum. This clutch wouldslip an amount dependent on the firing angle of triac 51.

The principles of the invention explained in connection with thespecific exempliiications thereon will suggest many other applicationsand modifications of the same. It is accordingly desired that inconstruing the breadth of the appended claims, they shall not be limitedto the specific details shown and described in connection with theexempliiications thereof.

Although various modifications might be suggested by those versed in theart, it should be understood that I wish to embody Within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of my contribution to the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are deiined as follows:

1. A drying apparatus comprising:

(a) means forming a treatment zone including tumbling means for tumblingarticles to be dried,

(b) driving means connected to the tumbling means,

(c) .control means for said driving means and comprising sensing meansassociated with the tumbling means and sensing the path of travel of thearticles to be dried and connected to the driving means to control itsspeed so that the articles to be dried travel in a path which is optimumfor drying.

2. A drying apparatus according to claim 1 and further characterized bymeans forming an air inlet and an air outlet for said treatment zone,air translation means for supplying a stream of drying air into saidtreatment zone through said air inlet and out through said air outletand said sensing means being placed in said air outlet.

3. Apparatus according to claim 1 wherein the sensing means istemperature responsive and controls the driving means as a function oftemperature changes in said treatment zone.

4. Apparatus according to claim 2 wherein the sensing means isresponsive to air pressure and controls the driving means as a functionof air pressure changes in the treatment zone.

S. Apparatus according to claim 1 wherein the sensing means isresponsive to radiant energy and controls the driving means as afunction of radiant energy changes in the treatment zone.

6. Apparatus according to claim 1 wherein the sensing means comprises apair of sensors with the lirst sensor mounted in a first position insaid treatment zone such that it has an output which varies as afunction of the moisture in the articles being dried, and the secondsensor is moved in a second position in said treatment zone such thatits output does not vary as a function of the moisture in the articlesto be dried when the articles are following the desired optimum pattern.

7. Apparatus according to claim 2 wherein said air outlet is positionedwithin the dryer such that articles travelling in an optimum path fordrying will be dispersed in the path of air directed into the outlet.

8. Apparatus according to claim 7 wherein the sensing means comprises apair of sensors with the first sensor mounted in the air outlet at aposition which is normally covered by articles travelling in an optimumdrying path, and the second sensor mounted in the air outlet at aposition which is normally not covered by articles travelling in anoptimum drying path.

9. Apparatus according to claim 6 and further characterized by a drivingmeans control circuit including a bridge circuit and wherein iirst andsecond sensors are mounted in the bridge circuit.

10. Apparatus according to claim 9, a tachometer connected to thedriving means and producing an output proportional to the speed of thedriving means and connected to the bridge circuit to energize it.

11. Apparatus according to claim 10 wherein the driving means controlcircuit includes a power gating circuit with its output controlling thedriving means and receiving an input from the bridge circuit so that thedriving means runs at a speed to maintain the articles being dried in anoptimum path.

12. Apparatus according to claim 11 wherein the power gating circuitincludes a power supply and gate means connected to circuit with thedriving means, and the gate means controlling power to the driving meansin response to the output of the bridge circuit.

13. Apparatus according tod claim 12, a dryer terminating circuitcomprising, switch means connected in circuit with the power supply, andthe dryer terminating circuit connected to control the switch means toturn the dryer off.

14. Apparatus according to claim 13, moisture content set means forminga portion of the dryer terminating circuit to turn the dryer off when apreset moisture level is obtained.

15. Apparatus according to claim 14, the power supply coupled to themoisture content set means, a relay connected to the switch means andthe moisture content set means, and a second gating circuit connected incircuit with the moisture content set means and relay and receiving aninput from the bridge circuit to turn the driving means olf when thepreset moisture content has been reached.

16. Apparatus for terminating the drying cycle of a tumble-type dryercomprising, a plurality of sensors mounted at distinct locations in thedryer for determining variable drying conditions as a function of thetumble pattern, and a dryer terminating circuit connected to saidsensors to turn the dryer oif when the conditions detected by thesensors reach predetermined values.

17. Apparatus according to claim 16 wherein the dryer has an air outletand iirst and second sensors are mounted at different locations withinsaid air outlet.

18. Apparatus according to claim 17 wherein the first and second sensorsare temperature responsive and the variable condition comprising changesin temperature.

19. Apparatus according to claim 17 wherein the first and second sensorsare pressure responsive and the variable condition comprising changes inpressure.

20. Apparatus according to claim 17 wherein the first and second sensorsare responsive to radiant energy and the variable condition comprisesvariations in the level of radiant energy.

21. The method of controlling the speed of a dryer wherein materials aretumbled by successively elevat.

ing the materials upwardly and gravitationally accelerating thematerials downwardly through a tumble pattern including a gravitationaltrajectory which includes the step of sensing the tumble pattern ofarticles within the drum at two distinct locations to develop a controlsignal as a controlling variable which is a function of changes in thetumble pattern.

22. The method of claim 21 wherein the tumble pattern is sensed as afunction of changes in pressure.

23. The method of claim Z1 wherein the tumble pattern is sensed as afunction of changes in temperature.

24. The method of claim 21 wherein the tumble pattern is sensed as afunction of changes in radiant energy.

25. The method of controlling a dryer as defined in claim 21 wherein thematerials are successively elevated and gravitationally accelerated byrotatably driving a drum and confining the materials in the drum andfurther characterized by controllingA the speed of the driving means asa function of changes in the tumble pattern so that the articles followan optimum tumble pattern for drying.

References Cited UNITED STATES PATENTS JOHN J. CAMBY, Primary ExaminerU.S. Cl. X.R. 34-52

